The present invention relates to a position detecting method and apparatus, and more particularly to an alignment apparatus mounted on a semiconductor exposure apparatus and an overlay inspection apparatus used to evaluate the alignment accuracy and to calculate an offset. The present invention is suitable, for example, for a position detecting method and apparatus used for global alignment to a wafer having plural shot areas and alignment marks corresponding to respective shot areas.
Projection exposure apparatuses used to manufacture semiconductor devices have been required to expose a circuit pattern on a reticle (or a mask) onto a wafer with higher resolution along with recent demands for finer and higher density circuits. The exposure apparatus is also required to facilitate an exposure process; for example, the flat processing technology, such as a chemical mechanical polishing (“CMP”) process, has been introduced for the increased depth of focus and easy exposure.
One important exposure parameter is the overlay accuracy that is accuracy in overlaying plural patterns on a wafer. The desired overlay accuracy needs highly precise alignment between a reticle and a wafer, and the alignment accuracy has become increasingly strict on demand for a finer circuit pattern. The necessary alignment accuracy is typically about one-third as large as a circuit's critical dimension; for example, 60 nm that is one-third as large as the current design width of 180 nm.
For an alignment between each shot on a wafer and a reticle, it is necessary to simultaneously and optically detect a circuit pattern on the reticle and an alignment mark that corresponds to each shot for exposure on the wafer, and to position the wafer relative to the reticle based on the detection result.
The common global alignment measures position coordinates of plural sample shots on the wafer, statistically processes the measurement values, calculates wafer's shift, magnification and rotational error, corrects the wafer coordinate, and moves to a next shot stepwise. The recently used advanced global alignment (“AGA”) develops the global alignment, relies upon the accuracy of an XY stage including a laser interferometer, measures wafer positions, calculates the wafer's magnification and rotational and shift amounts, and performs a statistic process, such as an abnormal value jump, etc.
Means for detecting an alignment mark includes a method for imaging an enlarged alignment mark through a microscope and for detecting a position of a mark image, a method for using a diffraction grating as an alignment mark, for detecting a phase of an interference signal through interference of the diffracted light, and for detecting a position of the diffraction grating, etc.
The improved overlay accuracy is vital for improved performance of semiconductor devices and enhanced manufacture yield. An introduction of special semiconductor manufacture technology, such as a CMP process, however, would cause alignment marks to have non-uniform shapes among wafers and shots, and disadvantageously deteriorate the alignment accuracy. This is because a demand for a finer circuit pattern has increased a difference in critical dimension between a circuit pattern and an alignment mark, and optimized process conditions, such as a film formation, etching, and CMP, for the finer circuit pattern (with a critical dimension from 0.1 to 0.15 μm), not for the wider alignment mark (with a critical dimension from 0.6 to 4.0 μm).
Expectedly, it will be increasingly difficult in the future to manufacture both a circuit pattern and an alignment mark on the same wafer surface without defects due to a demand for a finer circuit pattern, an introduction of a new semiconductor process, a larger wafer diameter up to 300 mm, etc. In addition, due to metal grains, a metal layer would face disadvantages in deteriorated S/N in an alignment signal and the lowered alignment accuracy.
If each alignment mark is designed to arrange, for example, four mark elements at regular intervals, the lowered alignment accuracy means that three mark-element intervals are detected differently. The conventional global alignment has not yet proposed a method for maintaining the predetermined alignment accuracy for scattering detection result of the alignment mark. Although the global alignment would be able to provide more reliable statistic calculations with detection information of alignment marks for all the shots on a wafer, this would lower the throughput and increase the cost.